Novel solid materials with desirable physical and chemical properties are constantly being sought for commercial applications. Economical, low temperature synthetic routes to new solids from readily available starting materials are of particular interest. Especially desirable attributes for novel materials are easy variability of physical and chemical properties and high thermal, storage and in-use stability.
One class of compounds used as starting material for new solids is the phosphazenes, compounds of the formula (NPX.sub.2).sub.n, with alternating phosphorus and nitrogen atoms. Soluble linear chlorophosphazene, [NPCl.sub.2 ].sub.n, is desirable as a primary source for making substituted phosphazene polymers (e.g., [NP(OR).sub.2 ].sub.n), many of which are useful as flame retardants and low-temperature elastomers. Solid hexachlorocyclotriphosphazene, [NPCl.sub.2 ].sub.3, undergoes polymerization at 200.degree. C.-300.degree. C. to [NPCl.sub.2 ].sub.n. The reaction is difficult to control because of cross-linking, air sensitivity, and the formation of insoluble gel products. The molecule [NPCl.sub.2 ].sub.3 is a potential hexa-coordinating ligand and might be expected to react with metal salts to form cationic metal-bridged polymers, [(ring)P--Cl--M.sup.II --Cl--P(ring)].sub.n, with useful properties. However, this approach does not work well in practice because [NPCl.sub.2 ].sub.3 is very water-sensitive. Reaction of [NPCl.sub.2 ].sub.3 with water results in formation of hydrochloric acid (HCl) which prevents formation of the metal-bridged polymer by competing protonation.